applicatie note

Phosphorous Content in Electroless Nickel Directly Measurable

Phosphorous, the concentration of which significantly influences the mechanical and magnetic properties of a coating, is incorporated when using typical methods for electroless or chemical deposition of nickel. Measurement of the phosphorous content has therefore been an issue ever since electroless Ni was first introduced for technical applications.

Until now, X-ray fluorescence analysis – widely used in the electroplating industry for coating thickness measurement and coating analysis – was only able to determine phosphorous concentration indirectly through evaluation of the substrate material’s signal, restricting the applicability of the technique to systems with substrates consisting of only one heavy element. Furthermore, a minimum coating thickness of about 4 µm was required.

However, using the FISCHERSCOPE® X-RAY with high resolution silicon drift detectors (SDD), the fluorescence signal of phosphorous can be measured directly, as long as the excitation conditions are selected correctly.

Figure 1: Coating model and schematic of the fluorescence excitation.

The information depth is very superficial: Fluorescence radiation from only the uppermost 1 µm enters into the spectra evaluation; therefore, interference from diffraction reflex can largely be excluded. The measurement uncertainty of the phosphorous content is about 0.5 mass per cent.

Figure 2: Overlap of 3 spectra with different phosphorous content. Height of the phosphorous peaks at 2 keV varies significantly.

Because measuring the thickness of a NiP coating is performed under different excitation conditions than determination of the concentration of P, these two measuring applications complement each other. Traceability can be ensured by using the respective calibration standards (with Fe, Cu, Al and PCB as substrate materials) from FISCHER.

The combination of state-of-the-art detector technology such as SDD, multiple excitations in various modes, and the powerful analysis software, WinFTM®, allows for reliable, accurate measurements of both coating thickness and phosphorous content of electroless nickel coatings on a wide variety of substrate materials. The FISCHERSCOPE® X-RAY XDV®-SDD unites all these performance features in one instrument.

Saving costs by using Inline Measurement for electroplating reel-to-reel applications

Electroplating reel-to-reel production lines need to maintain minimum and maximum tolerance limits for the applied coatings. To save costs, layers are coated as thin as possible - especially when using precious materials. However, a certain margin between the minimum limit and the nominal applied layer thickness is necessary to ensure the adherence of the lower tolerance limit due to process variations.

Usually, strips at the beginning and at the end of a reel are cut out manually and measured offline. This is time consuming for the staff and the reaction time is too long: If a tolerance limit is violated, it is too late to interfere since the coating process is finished and the reel already left the production line.

Inline measurement equipment – based on the x-ray fluorescence (XRF) principle – provides continuous data about the applied coating thickness and allows immedi­ate production process control. Feedback loops can be set up either with automatic communication between XRF instrument and coating line or manually by the operator. Therefore, the nominal applied thickness can be chosen to be closer to the minimum tolerance limit which significantly saves costs. Obviously, this is most effective for valuable metals but it also adds up for other coating materials. Additionally, products with rather tight tolerance limits can be manufactured only if there is a measurement system in the production line to determine the actual applied coating.

The following example where a gold (Au) coating of 2 – 4 µm needed to be applied shows the cost saving effects of such inline process control: Using offline instruments for quality control the nominal coating thickness was set to 2.8 µm Au to ensure not to violate the tolerance limit. After installing the inline measurement system FISCHERSCOPE® X-RAY 4000, the nominal coating thickness could be lowered to 2.3 µm Au.

Just by saving the 0.5 µm gold coating, the investment was amortized within half a year! Additionally, the production is now 100% documented. Every customer buying an electroplated reel gets a protocol with a statistical summary and a profile ensuring that the whole strip is coated properly within defined tolerance limits.

Fig. 1: Basic configuration of the FISCHERSCOPE® X-RAY 4000 with measuring head and PC.

Using the FISCHERSCOPE® X-RAY 4000 production cost can be lowered significantly by reducing material consumption, especially effective for precious materials, and by eliminating scrap production. Additionally, 100% of the applied coatings on the product are recorded and therefore traceable to comply with ISO9000 standards. For further information, your local FISCHER partner will be glad to assist you.

Measuring electroplated parts with user-defined inspection plans

Quality control plays an important role in rack plating. Narrow tolerance limits and strong demand for homogeneous coatings require precise measure­ments of the coating thickness according to clearly defined testing procedures. In addition, the measurement results should provide clues for potential process optimizations and, thereby, cost reductions.

Electroplated coatings must fulfill various criteria: functional coatings, for example, must provide a certain level of corrosion protection – requiring at least a minimum plating thickness – while adhering to defined cost restraints – meaning minimal material consumption. Moreover, the coating should be as homogeneous as possible, not only within a given rack, but also from rack to rack; this is important for both functional and decorative coatings. In addition, coating processes often must be executed within narrow tolerance limits. To check all these criteria systematically, test measurements should always be taken in the same spots, in the same way, regardless of who is currently executing the inspection. Furthermore, a number of workpieces must be tested, and that with as little effort as possible.

Fig. 1: A rack-plating jig sporting freshly electroplated parts

An effective way of controlling is to use individual inspection plans. For this purpose, FISCHER has developed its FISCHER DataCenter IP (inspection plan) software, which, utilized in combination with the DUALSCOPE® FMP100 coating thickness measurement instrument, allows a user to define inspection plans on the PC and download them onto the FMP100. The inspection plans guide an operator step-by-step, like a navigation system, through complex measurement tasks, providing exact instructions enhanced by images and text. The measurement spots are thus distributed evenly throughout the rack and set so that they capture all the critical areas (like edges). Via the pre-defined inspection plan, all measurement spots can be unambiguously identified. At the same time, a number of customer and process-associated data can be taken and later transferred into a measurement report.

Fig.2: Coating thickness measurement according to pre-defined inspection plans with DUALSCOPE® FMP100 and FISCHER DataCenter IP software. Images a) and b) show screenshots from the instrument, while c) shows a measurement report.

The readings are then downloaded directly to the PC for easy evaluation, archival and printing (with customisable templates). For this purpose a wide variety of analysis and statistic functions, as well as supporting graphical displays, are available.

The FISCHER DataCenter IP software and DUALSCOPE® FMP100 handheld instruments put the powerful tools of strategic quality control directly into inspectors’ hands: Step-by-step guidance through the complete measurement cycle not only minimizes human error, ensuring reproducible and comparable results on defined measurement spots, but qualifies these instruments for use even by non-technical operators. Structured measurement recording and extensive evaluation options further help to identify potential improvements in production processes. For more information please contact your local FISCHER representative.

Analysis of the metallic content of plating solutions

In order to apply coatings at a well-defined plating rate and with a well-defined composition, electro-plating companies must monitor and control the formulation of their plating baths very closely. For example, the metallic coatings (like AuCuCd, AuCuIn, RhRu or others) especially beloved in the jewelery industry must be applied absolutely homogeneously over the entire surface to ensure an even color finish.

The quality of metallic coatings depends heavily on the formulation of the plating bath, which consequently needs to be monitored. Compared with other methods, XRF (x-ray fluorescence) analysis of such solutions is straightforward: sample preparation is quick, and the only consumables required are small pieces of plastic foil, as opposed to other analytical methods where gases (Ar) or purified water are used.

All the FISCHER XRF instruments can be easily outfitted for analysing plating solutions by mounting the optional solution analysis cell (see Figure 2). First, the specialized cell is filled with the solution to be analyzed, then it is covered with a thin but robust Mylar foil and sealed with a plastic ring – all part of the solution analysis kit. Different cells are available which vary only in the material of the cell’s base from which they are made. Choosing the correct material can considerably improve the measurement performance. Matrix effects (Cl, SO4, CN,...) in the solution can be corrected via the absorption of fluorescence radiation of the cell’s base material (e.g. Mo or Ni).

Fig.1: Setup of the solution analysis cell. First it is filled with the solution, then covered by a Mylar foil and sealed with a plastic ring.

Due to the easy handling bath analysis can be carried out directly in the production without specially qualified personnel being required. Measurement results are available within minutes which provides short reaction times regarding changing the bath. In addition the cells are resistant against chemicals and can be re-used. There are no further operational costs involved.

FISCHER’s high-precision, fast and user-friendly XRF measurement systems are perfect for analyzing the metallic content of plating solutions. Equipped with the solution analysis cell they provide great time savings compared to other analytical methods. Please contact your local FISCHER representative for further information.